Since the beginning of the twentieth century, nitrogen (N) inputs to soils have increased tremendously worldwide, due to application of synthetic N fertilizers and manure in agricultural areas B. Zhang et al., 2017), and due to deposition of atmospheric N, coming mostly from fossil fuel combustion (Holland et al., 1999). These large N inputs to soils have not been balanced by N removal from soils through incorporation into plant biomass and crop harvest, resulting in large soil N surpluses in many places across the world, for